1. Field of the Invention
This invention relates to devices for automatically handling articles being molded. More specifically, this invention relates to devices for exercising living hinges of articles and closing lids of caps, while the articles and caps are in the mold.
2. Description of the Prior Art
The advantages of molding articles, both with respect to efficiency and cost, have been recognized for an extremely long period of time. More recently, materials have been discovered, such as certain plastics, from which living hinges can be molded. A living hinge, as used herein, is a flexible piece which is molded integrally with the components being hinged. This distinguishes from a typical hinge which is not molded integrally, with any pivoting taking place between two or more separate pieces, rather than within a piece. The low manufacturing costs of molded living hinges make them particularly advantageous. The low costs result from less critical tolerances necessary in a living hinge, and an elimination of the need for subsequent hinge assembly.
FIG. 1 shows a lid 10 connected to a cap 12 by means of a living hinge 14. Living hinge 14 includes pivots 16 and 18 and a spring 20, all of which are molded integrally with lid 10 and cap 12. Living hinge 14 is known as a snap-hinge, because lid 10 has a neutral position at which spring 20 has no effect. However, when lid 10 is not at the neutral position, spring 20 tends to force lid 10 away from the neutral position.
To close lid 10, it is pivoted toward cap 12, through the neutral position. Lid 10 is then depressed so that a skirt 22 fits within a wall 26 defining an aperture 24.
Living hinges are common in many other types of articles, also. For example, other types of caps with connected lids may employ living hinges. Also, tape cassettes which are molded in a single piece and then folded to form the housing employ living hinges. In fact, living hinges may be utilized wherever an inexpensive hinge is desired in association with a molded article.
However, care must be taken while molding a living hinge to be certain that the hinge works freely and easily. To ensure free movement, the hinge must be exercised while it is still hot. Otherwise, the hinge will be relatively inflexible upon cooling.
With caps such as illustrated in FIG. 1, a problem exists in ensuring a proper tightness between skirt 22 and wall 26. The problem arises from the fact that plastic employed in the molding process tends to shrink during cooling.
A common approach to ensure a proper fit is to employ different materials for lid 10 and cap 12. It is well known that different plastics shrink to different degrees. With some experimentation and calculation, it is possible to employ this characteristic to obtain a proper fit.
A much easier and more effective solution is to close lid 10 onto cap 12 while the plastic is still hot. If skirt 22 cools while inserted within aperture 24, the two parts tend to shrink together, thus forming a proper fit.
In the past, a mold for making caps such as illustrated in FIG. 1 usually had 8 or 16 cavities for making 8 or 16 caps simultaneously. To close lids 10, as the core and female mold sections separated, the shafts of air pistons, disposed within the mold (one associated with each mold cavity) would be activated to push lids 10 a small distance out of the mold. Air jets, one associated with each cavity, would then be activated to force the lids past their neutral positions.
When the mold sections had separated sufficiently, a rather large air sweep would come down between the sections and align with the mold cavities. Air pistons on the air sweep would then be actuated to cause the shafts of the air pistons to close the lids. The air pistons would then be deactivated and the air sweep would be removed from between the mold sections before the next molding cycle could begin.
This method of closing lids has proven to be slow and costly. A great deal of time is wasted in the mechanical motion of the air sweep. The air sweep must be constructed with a great deal of precision so that when it is lowered, it lines up accurately with the mold cavities. Because of the precision with which this large piece of equipment must be aligned, repairing and realigning the air sweep become seemingly continuous tasks.
Furthermore, with particularly small caps, it has been found that the air jets employed for pushing lids 10 beyond the neutral position do not have sufficient power to push lids 10 because of the small surface area of the smaller caps.